If you're suffering from a lack of sleep, then you might
experience very short blackouts called "micro-sleeps," according
to Wiseman. These are episodes where you involuntarily doze off
for a few seconds and are not aware of what's happening around
you. (This would be a considerable nuisance at work, but could be
potentially dangerous if you're, say, driving.)

To see if you're under-slept, Wiseman asks viewers to watch an
animated clip where a scene changes after a few seconds and then
flips back to the original scene. If you don't spot certain
things — like a bus switching from blue to green or disappearing
buildings — then you might be sleep deprived, he says.

We're not sure how valid this test is for sleep-deprivation since
a well-known Harvard psychology test, known as the "gorilla experiment," found that our minds
tend to miss a lot of obvious things going on around us (even a
giant gorilla strolling into the middle of a basketball game),
without even knowing it.

At any rate, Wiseman provides some other useful ways to determine
if you need more sleep. If you need an alarm clock to wake up,
fall asleep within 5 minutes of getting into bed, or drink a lot
of coffee during the day, then you should consider getting more
shut-eye.